α- d -Glucuronosyl-(1→3)- l -galactose, an unusual disaccharide from polysaccharides of the hornwort Anthoceros caucasicus

Acid hydrolysis of cell wall-rich material from thalli of the hornwort Anthoceros caucasicus yielded substantial amounts of an unusual disaccharide ( 1 ). Hydrolysis of 1 yielded only GlcA, Gal and unhydrolysed 1. Compound 1 was identified as α- d -Glc p A-(1→3)- l -Gal by 1 H and 13 C NMR spectroscopic analysis and by the susceptibility of its monosaccharide units to phosphorylation by enantiomer-specific kinases. Compound 1 was not detected in acid hydrolysates of other land plants including mosses, leafy and thalloid liverworts, lycopodiophytes and euphyllophytes; it was also absent from charophytes. The Anthoceros polysaccharide that yields 1 was partially extractable in cold aqueous buffer (pH 4.7) and Na 2 CO 3, but not in EDTA or NaOH, suggesting that it was not a typical pectin or hemicellulose. The yield of 1 from various polysaccharide fractions correlated with the yields of Xyl, suggesting a previously unreported polymer containing d -GlcA, l -Gal and Xyl. The existence of a unique polysaccharide in an evolutionarily isolated plant ( Anthoceros ) supports the view that major steps in plant phylogeny were accompanied by significant changes in cell wall composition.